Bluish-Green BMes2-Functionalized Pt<SUP>II</SUP> Complexes for High Efficiency PhOLEDs: Impact of the BMes2 Location on Emission Color

초록

New phosphorescent Pt-II compounds based on dimesitylboron (BMes(2))-functionalized 2-phenylpyridyl (ppy) N,C-chelate ligands and an acetylacetonato ancillary ligand have been achieved. We have found that BMes(2) substitution at the 4'-position of the phenyl ring can blue-shift the phosphorescent emission energy of the Pt-II compound by approximately 50 nm, compared to the 5'-BMes(2) substituted analogue, without substantial loss of luminescent quantum efficiencies. The emission color of the 4'-BMes(2) substituted Pt-II compound, Pt(Bppy)(acac) (1) can be further tuned by the introduction of a substituent group at the 3'-position of the phenyl ring. A methyl substituent red-shifts the emission energy of 1 by approximately 10 nm whereas a fluoro substituent blue-shifts the emission energy by about 6 nm. Using this strategy, three bright blue-green phosphorescent Pt-II compounds 1, 2 and 3 with emission energy at 481, 492, and 475 nm and Phi(PL)=0.43, 0.26 and 0.25, respectively, have been achieved. In addition, we have examined the impact of BMes2 substitution on 3,5-dipyridylbenzene (dpb) N,C,N-che-late Pt-II compounds by synthesizing compound 4, Pt(Bdpb)Cl, which has a BMes(2) group at the 4'-position of the benzene ring. Compound 4 has a phosphorescent emission band at 485 nm and Phi(PL)=0.70. Highly efficient blue-green electroluminescent (EL) devices with a double-layer structure and compounds 1, 3 or 4 as the phosphorescent dopant have been fabricated. At 100 cd m(-2) luminance, EL devices based on 1, 3 and 4 with an external quantum efficiency of 4.7, 6.5 and 13.4%, respectively, have been achieved.

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